Monolithic 2D high-power arrays of long-wavelength VCSELs

Abstract

InP-based, long-wavelength vertical-cavity surface-emitting lasers (LW-VCSELs) with buried tunnel junction are presented for high-power applications. Various studies of single-devices with large apertures and monolithically integrated two-dimensional VCSEL arrays are shown. The influence of aperture and array size on laser power, efficiency and divergence angle is investigated in detail. Unlike GaAs-based devices, large apertures are not favorable due to thermal issues. Accordingly, we focused on VCSEL arrays and derived scaling rules for optimum performance. This allows manufacturing high-power devices achieving continuous-wave (CW) optical powers in excess of 3 W at -11°C heat-sink temperature, circular far-field, low divergence angles around 20° and power densities of 130 W/cm2 at 1.55 μm. To the best of our knowledge, this is the highest power ever reported for a monolithic VCSEL array. At room temperature, more than 2 W is still available and high-temperature operation up to 70°C is applicable. The driving voltages around 1.2 V are significantly low, enabling single battery mobile operation. The wall-plug efficiency at room temperature exceeds 20% in a wide range. Addressing the array in sectors, we found that the array is very homogenous in performance with a standard deviation of less than 2.8%. Therefore, high-power applications can also be accomplished by VCSEL technology. As these novel devices with emission wavelengths beyond 1400 nm are less restrictive with respect to eye-safety, they are also favorable for free-space applications. Additionally, the devices may be used as concealed infra-red headlights that are invisible for all silicon-based detectors.